Technologies are known for extracting sound coming from a specific direction using a microphone array that includes multiple microphones. Specifically, when a user specifies a direction, a device that includes a microphone array extracts sound coming from the specific direction by subtraction of audio signals coming from other directions.
Devices that include a microphone array use PDM (pulse density modulation) digital microphones. Upon receiving sound, digital microphones convert the sound into digital audio signals by using PDM or, more specifically, convert the sound into digital audio signals in which a state is represented by “1” or “0” in each predetermined period.
Conventionally, a device that includes a microphone array subtracts the audio signals coming from one digital microphone from the digital audio signals coming from another digital microphone and outputs the result of the processing as digital audio signals (“0” or “1”). For example, when the device including the microphone array subtracts “0” from “1”, “1(=1−0)” is used as the processing results.
Microphone devices are disclosed that are omnidirectional when receiving sounds at low frequency ranges and directional when receiving sounds at high frequency ranges. Furthermore, technologies that relate to radio communication systems are disclosed.
Patent Document 1: Japanese Laid-open Patent Publication No. 04-318796
Patent Document 2: Japanese Laid-open Patent Publication No. 04-322598
Patent Document 3: Japanese Laid-open Patent Publication No. 03-504666
The conventional technologies have a problem in that audio quality deteriorates. Specifically, in the conventional technologies, because processing results are output as digital audio signals, when “1” is extracted from “0”, “0” is used as the processing result, not “−1 (=0−1)”. This causes an error and thus the original sound is not reproduced authentically, which lowers the audio quality.